There are a couple of Omaha articles here http://www.cardschat.com/poker-strategy.php.
Are u playing torneys or ring?
The FTP strategy guide has a chapter on tournement Omaha,i dont play much omaha but that capter was pretty easy to read and had some good stuff imo even thou it was way to short(only like 20pages but its a big book with good stuff on all the other games as well so its well worth it).
Only other book that had something on Omaha that if read is SS and since you allready read it i guess that not much help.
Here are a few books if heard are good but your gonna have to judge for your self since i havent read them so i cant really recament them.
High-Low-Split Poker, Seven-Card Stud and Omaha Eight-or-better for Advance players(obvs only if your playing O8).
Pot limit Omaha poker
Hold 'em Poker By Chiaffone